"It was just a really out-dated, misjudged and heavily biased presentation," the sixth-former told Pink News.

Chief executive of gay-rights campaigners Stonewall Ben Summerskill said: "This is a shocking breach of the school’s duty of care. It categorically shouldn’t be involved in such a live political issue, particularly in a way that demeans gay pupils. We’re sure students and parents will be upset that this school is creating deeply unpleasant environment for gay young people when so many other faith schools are doing a brilliant job tackling homophobia."

The British Humanist Association have dubbed the incident "outrageous".

"Not only might this break equalities legislation, it also breaks laws against political partisanship."

CES, which acts as a liason between the government and Catholic bishops, insisted the move was "purely religious and in no way political".

The CES spokeswoman added the BHA was "confused".

"They've got themselves into a muddle," she continued. "It is a very well established law that Catholic schools are allowed to teach Catholic beliefs. They have always been allowed to teach sex and relationships according to the Catholic religion."

"It is important children are taught about Catholic values. We are supporting marriage as it is currently defined. It is a positive affirmation, not negative."

The CES emphasised the St Philomena's was responsible for designing the presentation. Asked whether the "sign the petition" slogan on the presentation impeded free will, the spokeswoman replied: "It is not as dogmatic as people are suggesting".

"Children are in schools to have their minds opened to different things and to learn.

"Nobody was forced to sign the petition. It was just suggested to them."